The purpose of this proposal is to analyze the roles of several monoaminergic systems and the endogenous opioids in the regulation of the secretion of prolactin in male rats. The entire regulating mechanism is highly complex and, therefore, in order to evaluate the role of a specific system in a defined experimental situation it is necessary to delineate not only the influence of that particular system on the secretion of the hormone but also to determine what other systems are involved, what is the contribution of each of them to the overall hormonal response, how they are interconnected, and at what hypothalamic sites, which of the multiple neurotransmitter and opioid receptors are involved and what is the ultimate effector mechanism which leads to a stimulation or inhibition of prolactin secretion. To achieve this goal a variety of neuropharmacological interventions will be used in conjunction with determination of the distribution and metabolism of several monoamines (dopamine, norepinephrine, and serotonin) in microdissected hypothalamic and preoptic areas using high performance liquid chromatography. In some experiments animals with complete deafferentation of the mediobasal hypothalamus will also be used.